Method of supervising metallurgical and metal melting processes



July 11, 1961 wEvER AL 2,991,684

METHOD OF SUPERVISING METALLURGICAL AND METAL MELTING PROCESSES FiledJuly 51, 1956 3 Sheets$heet 1 July 11, 1961 w v ETAL 2,991,684

METHOD OF SUPERVISING METALLURGICAL AND METAL MELTING PROCESSES FiledJuly 31, 1956 5 Sheets-Shet 2 L r L s; 1 Q i L g l if July 11, 1961 F.WEVER ETAL 2,991,684

METHOD OF SUPERVISING METALLURGICAL AND METAL MELTING PROCESSES FiledJuly 31, 1956 3 Sheets-Sheet 5 f it tates ate 1 1;

2,991,584 Patented July 11, 1961- many Filed July 31, 1956, Ser. No.601,151 priority, application Germany Aug. 2, 1955 3 Claims. (CI. 88-14)For supervising the course of metal melting processes, especially steelmelting processes, samples are continuously taken and analysed duringthe course of the melting. The results are the more valuable forfollowing the course of the reaction the more quickly they are obtained.Consequently, automatic spectroscopic analysis apparatus has recentlybeen used for this purpose, and with this apparatus most of the alloyingelements can be analysed in a few minutes. A number of elements whichare important for appreciating the course of the metallurgical processcannot, however, be quickly analysed spectroscopically. In particularthe elements oxygen, hydrogen and nitrogen cannot be detected by theusual spectroscopic apparatus. The determination of these elements bythe processes hitherto usual, however, takes up so much time that thesamples taken for supervising the course of the reaction in the meltingfurnace and for determining the result of deoxidation treatment whichusually takes place in the ladle can no longer be evaluated.

The usual method of determining the gases oxygen, hydrogen and nitrogenin steel and other metals is by melting the metal in a carbon crucibleunder a high vacuum i.e. a hot extraction process. The oxygen escapesfrom the super-heated melt in the vacuum in the form of carbon monoxideand hydrogen and nitrogen escape in elementary form. In addition gasessuch as S H 8, CO H O, CN nitric oxide, hydrocarbons and other gases areliberated. This evolution of gases from steel melts takes place at atemperature of 1600-1700" C. very quickly depending on the size of thesample, for example, with samples of a few grams in 1-3 minutes. Thegases are evolved still more quickly at 1400 C. from copper melts. Thegases liberated are usually brought to atmospheric pressure with the aidof a diffusion pump and a following collecting pump and are thereafterexamined in a gas analysis apparatus. With the known apparatus, thecompression and analysis take a longer time than the extraction, so thatin this part of the examination expensive time is lost and consequentlythe process is unsuitable for the analysis of preliminary samples.

The invention relates to a process for supervising the course of metalmelting processes, especially steel melting processes, and according tothe invention, the gases, after being liberated at pressures of 001-5mm. Hg, preferably at pressures between 0.1 and 1 mm. Hg, are caused toglow by a high frequency discharge and the light emission in acharacteristic range is measured automatically and without loss of timeby a spectroscopic analysis apparatus. In addition, for measurement ofthe total amount of gas, the pressure is fixed.

Experiments have proved that analysis of the three most important gases,namely carbon monoxide, hydrogen and nitrogen can be carried out side byside, in which case, however, certain corrections must be made whichtake into account the reaction of the gases with one another in the highfrequency field.

The measurements can be carried out in a current of gas which, however,is held at constant pressure in a section in which it is activated bymeans of two valves.

Claims Under these conditions the reaction of the gases with one anotherneed not be taken into account and also other gases can be included inthe mixture.

The invention will now be described with the aid of the accompanyingdrawing, in which:

FIG. 1 is a diagram showing the main parts of an apparatus for carryingout the method of the invention;

FIGS. 2, 3 and 4 are curves and diagrams showing the results of theexamination.

Referring to the drawings, the reference letter designates an extractionfurnace, B a diffusion pump which, however, may be omitted, C anactivating vessel having inlet and outlet valves D and B respectivelyand a coil F for high frequency activation of the gas. The referenceletter G designates a pressure measuring apparatus and H a spectroscopicanalysis apparatus.

In the vessel C the gas activation can be kept so constant that therelative intensities need not be meas-' ured, as is usual, but analysisby measuring the absolute intensities of the individual components ispossible. This considerably simplifies the apparatus and reduces itscost. In addition to maintaining the high frequency field constant andregulating the pressure, Water cooling of the high frequency electrodesis also necessary.

The time required for carrying out the analysis according to theinvention is extremely short. Directly after the gases enter theactivating vessel C the intensities of the individual spectral lineswhich are used for the analysis are indicated. The lines which are usedfor the analysis are in the case of hydrogen the lines H,,, H,,, and H,whereas, for the analysis of carbon monoxide and nitrogen bands in therange of 3000-8000 A. are used, those for CO being preferably around4510 A., and those for nitrogen being in the region of 7000A.

In all vacuum metallurgical processes the supervising method of theinvention is of considerable importance because it is now possible toconnect the gas analysis part of the apparatus beginning with thediffusion pump or the gas activating vessel directly to any vacuummetallurgical installation, for example to a high frequency vacuumfurnace or to a vacuum casting installation and continuously to analysethe gas given off from the melt.

The method of the invention instead of being carried out in theabove-mentioned manner at constant gas pressure can also be carried outin a different manner. Thus, experiments have shown that the lightemission of all the gases investigatedwith a constant activation fieldpasses through a maximum at pressures of approximately 10- mm. Hg. Thisknowledge can now be used for a further simplication of the gas analysiswhich will now be explained with the aid of FIG. 1.

The gases from the extraction furnace A or the diffusion pump B arefirst introduced at a pressure of 01 mm. Hg into the vessel C and thepressure is then lowered by evacuation through the valve E to 0.1 mm.Hg. The intensities of the spectral lines, therefore, pass through theirmaxima. The maximum intensities correspond to the concentration of themixtures. They are separated, measured photoelectrically and registered.In this case it is no longer neces sary to keep the pressure in thevessel C constant which considerably facilitates the direct analysisprocess. A measurement of the total gas quantity can also take placehere in known manner in the chamber G behind the valve E.

When the apparatus is directly connected to a vacuum metallurgicalinstallation, the escaping gases can be continuously analysed byadmitting gas in rhythmic sequence through the valve D, which isautomatically controlled, so that the pressure in the chamber C exceedsthe maximum pressure of about 0.1 mm. Hg. The gas is continuously thenwithdrawn through the valve E until the pressure is gases in the gasbelow the maximumpressure. In this way the emission continuously passesthrough its maximum at short intervals of time and thus the compositionor the gas may be continuously registered and its alterations followed.

This continuous gas analysis can also be used for a series of othergases, for example carbon monoxide, hydrogen, halogens as well as for alarge number of compounds of hydrogen with carbon, nitrogen, phosphorusand silicon amongst others as well as with volatile compounds of thehalogens. The method can, therefore, be used not only for supervisingmetallurgical reactions but also for supervising chemical processes. Thespectral conditions, especially the resolving power of the spectroscopic apparatus which is used should be adapted to suit the conditionsat the time.

Various examples of the use of the new process will now be given toexplain how the apparatus is calibrated and how the analysis is carriedout both at constant pressure in the activating vessel C, as well aswith the fall in intensity maximum with falling pressure. The gasmixtures analysed all contained hydrogen in addition to nitrogen andcarbon monoxide.

Example 1 For calibrating the apparatus difie-rent mixtures of puregases were made and after being thoroughly mixed were conducted throughthe apparatus. The inlet and outlet valves were regulated in such a waythat there was a constant pressure of 0.3 mm. Hg in the activatingvessel C. After this the intensities of the spectral lines used foranalysis in the spectrum of the activated gases were measured a numberof times at short intervals and registered.

For calibrating purposes, the nitrogen bands at 3943/98 A. and thecarbon monoxide bands at 4510 A. were used. FIG. 2 shows by Way of exampe the individual intensities measured for the nitrogen bands withdifferent nitrogen contents, namely 10, 20, 30, and 40% N FIG. 3 showsthe nitrogen calibration curve resulting therefrom. The apparatus wasalso calibrated in a similar manner for carbon monoxide and forhydrogen.

In the analysis of unknown gas mixtures originating from any gasapparatus the contents determined in the usual manner were compared withthose obtained by spectroscopic analysis. The following is a comparativeexample of the results obtained:

N2, percent 00, percent chemical spectroscopic chemical spectroscopicExample 2 tered and FIG. 5 shows the corresponding calibration curve.Since the measurement made in this way is independent of the pressure,the variations are smaller than when measuring with constant pressure.The following table gives comparative results for chemical andspectroscopic analysis:

N2, percent 00, percent chemical spectroscopic chemical spectroscopic Weclaim:

1. A method of testing a metallurgical process by taking samples of amelt, melting said samples in a vacuum and determining the oxygen,hydrogen and nitrogen gases contained therein and extracted by saidvacuum melting, which comprises energizing said vacuumextracted and thusliberated gases so as to cause them to glow by activating them in a gasdischarge vessel at a pressure of 0.01 to 5 mm. Hg by a constanthighfrequency field and analyzing the light emission spectroscopical-ly.

2. A method of testing a metallurgical process by taking samples of 'amelt, melting said samples in a vacuum and determining the mixture ofoxygen, hydrogen and nitrogen gas contained therein and extracted bysaid vacuum melting, which comprises energizing said vacuum-extractedand thus liberated gas and causing it to glow by activating it in a gasdischarge vessel at a pressure of 0.01 to 5 Hg by a constanthighf-requency field, lowering the pressure in said vessel from a valueabove that at which the light emission of the gas is at a maximum to avalue below that at which the light emission is at a maximum anddetermining the composition of the gas mixture from the maximumintensities of its spectroscopically measured light emission.

3. A method of testing chemical reactions, which comprises removinggases evolved during said reactions therefrom, causing them to glow byapplication of a. constant high frequency field in a discharge vessel,maintaining the pressure therein above that pressure at which the lightemission of said gases is at a maximum, followed by lowering thatpressure below the maximum light emission, and determining thecomposition or said gases spectroscopically from the maximum intensitiesof their light emission, replacing the gases by a fresh supply of gasesand repeating the process.

References Cited in the file of this patent UNITED STATES PATENTS2,339,754 Brace Jan. 25, 1944 2,393,650 Metcalf Ian. 29, 1946 2,544,078Glassbrook Mar. 6, 1951 2,670,649 Robinson Mar. 2, 1954 2,708,387 Broidaet a1 May 17, 1955 2,795,132 Boehme et al. June 11, 1957 FOREIGN PATENTS329,111 Great Britain May 15, 1930 706,535 Great Britain Mar. 31, 1954

1. A METHOD OF TESTING A METALLURGICAL PROCESS BY TAKING SAMPLES OF AMELT, MELTING SAID SAMPLES IN A VACUUM AND DETERMINING THE OXYGEN,HYDROGEN AND NITROGEN GASES CONTAINED THEREIN AND EXTRACTED BY SAIDVACUUM MELTING, WHICH COMPRISES ENERGIZING SAID VACUUMEXTRACTED AND THUSLIBERATED GASES SO AS TO CAUSE THEM TO GLOW BY ACTIVATING THEM IN A GASDISCHARGE VESSEL AT A PRESSURE OF 0.01 TO 5 MM. HG BY A CONSTANTHIGHFREQUENCY FIELD AND ANALYZING THE LIGHT EMISSION SPECTROSCOPICALLY.